Fix parse error on block sequences with child flow style container nodes

[fktn-k]

This PR has fixed parse errors which the current parser emits on a block sequence containing child flow style containers (either sequence and/or mapping), like the following valid YAML snippet (based on the official YAML test suite YD5X):

# child flow sequences
- [username, identifier, score]
- [booker12, 9012      , 61.25]
- [grey07  , 2070      , 84.50]

# child flow mappings
- {foo: false, null: 123}
- {true: 3.14, bar: [0x30,0o30]}

While modifying implementation to fix the above issue, the way of managing parse contexts has also been corrected by adding the variation of parse context states.

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• Changes are described in the pull request or in a referenced issue.
• The test suite compiles and runs without any error.
• The code coverage on your branch is 100%.
• The documentation is updated if you added/changed a feature.

Please don't

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[github-actions]

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Pull Request Test Coverage Report for Build 8915291691

Details

• 123 of 123 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 8899528587:	0.0%
Covered Lines:	3574
Relevant Lines:	3574

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